Method of producing etched printing plates



Patented Sept. 1, 1953 UNITED STATES PATENT OFFICE METHOD OF PRODUCING E'ICHED PRINTING PLATES No Drawing. Application December 9, 1949, Serial No. 132,200

7 Claims. 1

This invention relates to photography and more particularly to a method of obtaining a resist of gelatin suitable for use in. making intaglio printing members. The invention also relates to the preparation of such printing members using the resists.

An object of this invention is to provide improvements in the art of making gelatin resists. A further object is to provide a simple and effective method of making gelatin resists and etched printing members therefrom which can be practiced by the ordinary technician with conventional equipment. Still other objects will be apparent from the following disclosure.

The invention in one of its -broader aspects involves exposing a flexible photographic film element having an outer light-sensitive gelatino silver halide emulsion layer and a hydrophobic support through a screen for a suitable time and then through a continuous tone positive, or vice versa. Other conventional types of screens and sequences of exposure can be used. The exposed film is then developed in an aqueous hardening developer solution, s. g, one containing pyroallol, a small amount of a bisulfite and a rela tively large amount of a carbonate whereby the gelatin is tanned at thepoints of the silver 'deposits and proportionally to the density of such deposits. The developed filmis fixed in a nonhardening fixing bath, washed sufiiciently to remove the fixer, bleached in a non-hardening bleach bath containing a water-soluble salt of .a metal compound producing an insoluble (silver salt image readily soluble :in .thiosulfate .solu-- tions, washed and dried. The bleaching :stepcan be eliminated in a modification 'of the process just described. The :ge'latin surface :ofthe film is pressed into contact with .a' wet surface of 1a metalprinting member, e.'g., a copper,;aluminum or zinc plate or cylinder, the support t=removed in some suitable manner leaving the gelatin image-bearing layer firmly adherent to the metal surface. The unhardened gelatin is washed off with hot water leaving a gelatin resistof varying thickness containing.silver'salts. Whenthe support is a composite one and consists of several layers, e. g., a permanentsupport, strippinglayer and temporary support, the removal requires successive steps.

The surface of the printing plate or cylinder is then etched by treating the gelatin relief image or resist with an acidic solution whereby the image is etched into the surface of the metal. The residue of the hardened gelatin resist is then washed off by a suitable solution, e. g., an

2 aqueous acetic acid solution of moderate to high concentration. Such solutions may also contain a relatively high concentration of sodium chloride.

The developed photographic layer can be bleached to form an insoluble silver salt image, e. g., a .silver halide, .dichromate or ferricyanide image, preferably the latter. The preferred alkali metal .ferricyanide bleaching solutions are especially useful when they contain a mixture of borax and boric acid.

Various types of photographic film elements may be processed in accordance with the method outlined above but the invention isespecially useful with dry-stripping films wherein the gelatino silver halide layer is coated onto a relatively thin permanent support which is in turn adhesively joined 'to a temporary support by means .of a dry-stripping layer. The supports should be made of .a hydrophobic material so that the resulting composite element will have good dimen sional stability. The permanent support should be readily soluble in commercial solvents .so it maybe eifectively removed from the gelatin layer adhering to the surface of the metal printing member by 'a simple washing operation. The gelatino silver halide emulsion layer is generally not directly coated onto the film support .but first a thin gelatin substratum is applied in order to improve the anchorage.

When a cellulose ester .film, e. -g., cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose :nitrate, cellulose propionate, etc., is used in the support for the -gel atino silver halide emulsion layer suchasuppor-t film can readily be removed with-commercialsolvents for such esters. Mixtures of acetone and ethyl or methyl alcohol and mixtures of acetone and the monomethyl or monoethyl ether of ethylene glycol are especially useful. Acetone can be used alone if desired but because of its high degree "of volatility .is .somewhat difiicult to handle. The monoethyl ether of ethylene glycol alone is an excellent single solvent for the permanent support.

The silver ferricyanide, etc, salts which are present in the bleached gelatin layer render a distinct image visible on the metal plate or ,cylinder. In addition, the salts control the rate and degree of penetration .of the etching solution in proportion to the density of the silver salts presentand enable oneto obtaina good reproduction of theoriginal-object field .on the surface of the metal plateorcylinder. The silver ferricyanide salts, moreover, seem to :have a catalytic effect on the etching solution since one can adequately etch copper plates with one concentration of iron perchloride solution in contrast to the five different concentrations which are commonly used.

Fugitive or non-fugitive dyes may be present in the gelatino silver halide layer of the stripping film, if desired, but good results can be obtained with layers free from dyes.

The invention will be further illustrated but is not intended to be limited by the following examples. I

Example I A photographic stripping film consisting of a cellulose acetate film base bearing on one surface in order a layer of cellulose nitrate, a thin substratum of gelatin and a gelatin backing layer and on the other surface in order a stripping layer composed of a mixture of water-insoluble ethyl cellulose and cellulose nitrate, a cellulose nitrate film, a thin gelatin substratum and a lightsensitive gelatino-silver halide emulsion layer was exposed through a gravure screen (150 line-2:1) for 30 seconds at 10 foot candles and then exposed through a continuous tone positive image for a period of 10 to 30 seconds. The exposed film was then processed as follows:

1. Developed for three minutes at 65 F. in a solution made by mixing 1 part of solution A with 2 parts of solution B.

2. Rinsed in water at 65 F. for 30 seconds;

3. Treated for one minute in an aqueous bath of 10% sodium bisulfite;

4. Washed in water at 65 F. for three minutes;

5. Fixed for three minutes in 20% sodium thiosulfate solution;

6. Washed for five minutes in water at 65 F.;

'7. Bleached for five minutes in a solution made by admixing the following components:

Grams Potassium ferri-cyanide 60 Borax 5 Boric acid Water to 1 liter.

8. Washed in water at65 F. for a period of minutes and then dried at 68 F. at 55% relative humidity.

The gelatin surface of the bleached film was squeegeed into contact with the surface of a wet copper plate. The temporary support which was outermost was then stripped from the cellulose nitrate film support. The latter support was removed by dissolving it in a washing solution composed of 60% acetone and 40% ethyl alcohol. A gelatin relief image which constituted a gelatin resist was formed by washing the gelatin layer with water at 125 F. for five minutes. The resist was dried and then treated with 38 Baum iron perchloride for a period of about 17 minutes whereby a good reproduction of the photographic image was etched into the surface of the copper plate. The residue of the relief image was Washed off with 28% aqueous acetic acid.

Example II A photographic stripping film of the kind described in Example I was exposed as described in such example except that a conventional screen having a space to line ratio of 2 /2:1 was used. The exposed film was then processed and used to make an etched plate by the procedure described in Example I, except that the residue of the relief image was washed off by means of 28% aqueous acetic acid containing a large amount of sodium chloride.

Example III A photographic stripping film of the type given in Example I was exposed, developed and washed as described in that example including steps (1) and (2).

3. Fixed for three minutes in 20% sodium thiosulfate solution;

4. Washed for five minutes in water at 65 F.;

5. Bleached for five minutes in a solution made by admixing the following components:

Grams Potassium ferri-cyanide Borax 5 Boric acid 10 Water to 1 liter.

6. Washed in water at F. for a period of 15 minutes and then dried at 68 F. at 55% relative humidity.

The gelatin surface of the bleached film was squeegeed into contact with the surface of a wet copper plate. The temporary support which was outermost was then stripped from the cellulose nitrate film support. The latter support was removed by dissolving it in a washing solution composed of 60% acetone and 40% ethyl alcohol. A gelatin relief image which constituted a gelatin "resist was then made by washing the gelatin layer with water at F. for five minutes. The resist was dried and then treated with 38 Baum iron perchloride for a period of about 17 minutes, whereby the photographic image was reproduced on the surface of the copper plate. The gelatin residue was washed off the plate after the manner described in Example II.

Example IV A film of the type given in Example I was ex posed and processed to a resist as described in that example except that in place of developing the film in the mixture of solutions A and B it .was developed in solution A for two minutes and in solution B for one minute. After the development was completed the film was processed by using steps 3 through 8 of Example I. The gelatin relief image was treated with acid and the copper plate etched and cleaned as described in that example with similar results.

Example V A film of the type given in Example I was exposed and processed as described in that example except that a fixing bath was used containing 25 grams of boric acid and 250 grams of sodium thiosulfate per liter and after fixing the film was washed and dried, omitting the bleaching step (7) in that example. Etching was accomplished by using a 43 Baum bath for two minutes, 41 Baum five minutes, 39 Baum six minutes and 38 Baum for six minutes.

When brass, aluminum, stainless steel or zinc plates are substituted for the copper plates in accepts th foregoing examples one-obtains similar results.

The invention is not limited to the particular bleach baths of the rorego'ing examples as other suitable' baths whichresult in a silver rerricyanide or a silver "bichromate, -etc., image can be substituted. A'suitahle bath has the to'llowing composition:

Potassium .ferricyanide-, grams .50 Ammonium hydroxide, conc.- .cc 5 Water to v1 liter.

Another suitable ibleach bath which :has a harden'ing action has the tormula:

Potassium bic'hromate i ,grams 2'0 Hydrochloric acid, conc. i cc Potassium bromide grams .5

Water to 1 liter.

similarly, the invention .is not limited to the particular developer solution rior developing the silver halide :image which is described in Example Various other conventional developers can he used with :similar results. Changes :in contrast, for example, can he accomplished by changing the amount :of carbonate in solution B of the developer in Example '1. Thus, the

amount of sodium carbonate may be varied from to 260 :grams ,per liter. .At the lower =concentrations the resist is lower in contrast than a in Example I and when amounts greater than 100 grams are used the contrast :is higher. Potassium carbonate can be used in equivalent amount. The development periods can be varied over a moderate range .as apparent to those skilled in the art.

.In the washing operation following bleaching when the gelatin relief image or resist is formed the temperature of the water and the time of treatment may vary. Temperatures from 105 F. to 145 and times from three minutes to 3-0 minutes are practical ranges.

Especially :good results are obtained with ffixing baths which contain material amounts of boric acid, e. g., 1-5 to grams :per liter in addition to the fixing agent.

The etching treatment may be varied depending upon the particular .type of metal plate or cylinder used. The etching may he conducted,

with a single solution or in several solutions of different strength, e. g., iron perchloride solutions varying from Baum and ending with Baum 35 can be used. An advantage of the present invention is that a single Baum iron perchloride solution preferably about 38 can be used instead of the five solutions used by photoengravers.

In addition to the procedures described above the films may be processed as follows:

1. The film may be exposed, developed in a hardening developer, placed in a stop bath, washed and dried.

2. The film may be exposed, developed in a hardening developer, fixed in a non-hardening fixer, washed and dried.

3. The film may be exposed, developed in a hardening developer, bleached, fixed, washed and dried.

The invention is especially useful in processing the dry stripping films of the types described in copending application Ser. No. 125,198, filed November 3, 1949. It is not limited to such stripping films, however, but can be used with various other types. Suitable additional ones are described in U. S. Patents 2,266,435, 2,275,617 and 6 2,3913%. Pigments such as iron oxide should beavoided in the films, "howeverfbecausehardening developers are "reduced by them and cause general overall fhardening.

The processes of this invention have the advantage that the usual carbon tissues used in the gravure industry 'can beeliminalted with their attendant disadvantages. An important advantage of the invention is that it enables the tech nic'ian in the gravure art to use one etching :solution "with the same result previously obtained with several. A further advantage is that the silver salts enable the technician to view the nature of the photographic reproduction before the etching operation :is carried out. -Still other obiects *w-i-ll be apparent to those skilled in the art.

As many widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be "understood that the invention is not to be limited except "as defined by the claims.

What is claimed is:

1. A process o'fmaki-ng an etched printing plate from adry-stripping film having a gelatino silver halide emulsion layer carried by a thin hydrophobic -cellu'lose derivative support which is adhesively joined-to a temporary supportby a drystr i-ppi-n'g layer, comprising exposing the emulsion layer separately through a screen and to a photographic picture, developing the exposed film in 'a hardening developer, fixing said developed film, bleaching the resulting film with an aqueous solution containing a water-soluble alkaii metal salt of an acid which "forms an insoluble silver salt image readily soluble in thiosulfate solutions, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the wet surface of ametal printing-member, stripping the "temporary support from the remaining support, dissolving the latter support, washing the unharderred gelatin from the gelatin layerwhereby a relief image is formed and treating the relief image with an acid etching solution whereby an image is etched into the surface of said printing member.

A process as set forth in claim 1 wherein the support is dissolved with ethylene glycol monoethyl ether.

3. A process of making an etched-printing plate from a dry-stripping film havin a gelatino silver halide emulsion layer carried by a thin hydrophobic cellulose derivative support which is adhesively joined to a temporary support by a drystripping layer, which comprises exposing the emulsion layer separately through a screen and to a photographic picture, developing the exposed film in a hardening developer, fixing said developed film, bleaching the resulting film with an aqueous solution containing an alkali metal ferricyanide, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the wet surface of a metal printing member, stripping the temporary support from the remaining support, dissolving the latter support, washing the unhardened gelatin from the gelatin layer whereby a relief image is formed and treating the relief image with an acid etching solution whereby an image is etched into the surface of said printing member.

4. The process of making an etched printing plate from a dry-stripping film having a gelatino silver halide emulsion layer carried by a thin hydrophobic cellulose derivative support which is adhesively joined to a temporary support by a dry-stripping layer, which comprises exposing the emulsion layer separately through a screen and a photographic image,- developing the exposed film in a hardening developer, fixing said developed film, bleaching the resulting film with an aqueous solution containing an alkali metal ferricyanide, borax and boric acid, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the Wet surface of a metal printing member, stripping the temporary support from the remaining support, dissolving the latter support, washing the unhardened gelatin from the gelatin layer whereby a relief image is formed and treating the relief image with an acid etching solution whereby an image is etched into the surface of said printing member.

5. The process of making a resist from a drystripping film having a gelatino silver halide emulsion layer carried by a thin hydrophobic cellulose derivative support which is adhesively joined to a temporary support by a dry-stripping layer, which comprises exposing the emulsion layer separately through a screen and a photographic image, developing the exposed film in a hardenin developer, fixing said developed film, bleaching the resulting film with an aqueous solution containin an alkali metal ferricyanide, borax and boric acid, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the wet surface of a metal printing member, stripping the temporary support from the remaining support, dissolving the latter support and washing the unhardened gelatin from the gelatin layer whereby a relief image is formed.

6. A process of making an etched printing plate from a dry-strippingfilm having a gelatino silver halide emulsion layer carried by a thin hydrophobic cellulose derivative support which is adhesively joined to a temporary support by a drystripping layer, which comprises exposing the emulsion layer separately through a screen and a photographic image, developing the exposed film in a hardening developer, fixing said developed film, bleaching the resulting film with an aqueous solution containing an alkali metal ferricyanide, borax and boric acid, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the wet surface of a metal printingmember, strippingthe temporary support from the remaining support, dissolving the latter support, washing the unhardened gelatin from the gelatin layer whereby a relief image is formed and impregnating the relief image with an iron perchloride solution of 35 to Baum whereby an image is etched into the surface of the printing member.

7. A process of making an etched printing plate from a dry-stripping film havinga gelatino silver halide emulsion layer carried by a thin hydrophobic cellulose derivative support which is adhesively joined to a temporary support by a drystripping layer, which comprises exposing the emulsion layer through a screen and to a photographic picture, developing the exposed film in a hardening developer, fixing said developed film, bleaching the resulting film with an aqueous solution containing an alkali metal ferricyanide, borax and boric acid, drying the bleached film, pressing the bleached gelatin silver salt layer into contact with the wet surface of a copper printing member, stripping the temporary support from the remaining support, dissolving the support, washin the unhardened gelatin from the gelatin layer whereby a relief image is formed and impregnating the relief image with an iron perchloride solution of 38 Baum whereby an image is etched into the surface of the printing member.

MAHLON RICHARD BOYER. ARTHUR WILLIAM GRUMBINE.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Clerc, Photography, 2nd edition, 1937, Pitman 8; Sons, page 278. 

1. A PROCESS OF MAKING AN ETCHED PRINTINNG PLATE FROM A DRY-STRIPPING FILM HAVING A GELATINO SILVER HALIDE EMULSION LAYER CARRIED BY A THIIN HYDROPHOBIC CELLULOSE DERIVATIVE SUPPORT WHICH IS ADHESIVELY JOINED TO A TEMPORARY SUPPORT BY A DRYSTRIPPPING LAYER, COMPRISING EXPOSING THE EMULSION LAYER SEPARATELY THROUGH A SCREEN AND TO A PHOTOGRAPHIC PICTURE, DEVELOPING THE EXPOSED FILM IN A HARDENING DEVELOPER, FIXING AND DEVELOPEN FILM, BLEACHING THE RESULTING FILM WITH AN AQUEOUS SOLUTION CONTAINING A WATER-SOLUBLE ALKALI METAL SALT OF AN ACID WHICH FORMS AN INSOLUBLE SILVER SALT IMAGE READILY SOLUBLE IN THIOSULFATE SOLUTIONS, DRYING THE BLEACH FILM, PRESSING THE BLEACHED GELATIN SILVER SALT LAYER INTO CONTACT WITH THE WET SURFACE OF A METAL PRINTING MEMBER, STRIPPING THE TEMPORARY SUPPORT FROM THE REMAINING SUPPORT, DISSOLVING THE LATTER SUPPORT, WASHING THE UNHARDENED GELATIN FROM THE GELATIN LAYER WHEREBY A RELIEF IMAGE IS FORMED AND TREATING THE RELIEF IMAGE WITH AN ACID ETCHING SOLUTION WHEREBY AN IMAGE IS ETCHED INTO THE SURFACE OF SAID PRINTING MEMBER. 